Wiki info about Yak-3P

A single-seat monoplane fighter with a composite construction, retractable landing gear and a closed cockpit.
A modification of the Yak-3 fighter with improved armament consisting of the 20 mm Berezina B-20M engine cannon and two synchronized 20 mm Berezina B-20S cannons installed instead of the synchronized machine guns. Since the B-20 cannons were modifications of UB machine guns with an increased-caliber barrel, the fighter's design required practically no changes. The aircraft's empty weight increased by only 11 kg, while the weight of its armament and ammunition ended up even lower than that of the Yak-3 with its ShVAK cannon and two large-caliber UB machine guns. The change in weaponry had no detrimental effect on the aircraft's flight characteristics.
The Yak-3P fighter was armed with one B-20M engine cannon with 120 shells and two synchronized B-20S cannons with 130 shells each. All the cannons were fired using a compressed-air electric mechanism. The PKI-1 sight replaced the PBP-1A sight.
The Yak-3P had a strengthened airframe (particularly the wing), and clasps were installed on the extra landing gear panels. The aircraft received the new RSI-6M radio.
The experimental Yak-3P completed its maiden flight on 23 March 1945. The fighter went into series production at several aircraft plants only a few days before the end of the war, so it never reached the front. From August 1945 and to the end of series production, all Yak-3 fighters were built exclusively to the standard of the Yak-3P. In total, 596 were produced between April 1945 and the middle of 1946. The last of them served until 1950.